Using quantities in dates is currently not validating correctly.

[MatthijsvdWielen]

Executing the examples in https://hl7.org/fhirpath/N1/#subtraction-2, provides an error in the FHIRPath playground.

This can be worked around by adding a '+' to the fhirpath.

Originally posted by @MatthijsvdWielen in https://github.com/FirelyTeam/firely-net-sdk/issues/2431#issuecomment-1744681689